The present invention relates to a switching regulator, and more particularly to a switching regulator suitable for mobile devices such as mobile phones, and note-type personal computers.
The requirements for size-down and weight reduction of mobile devices such as mobile phones, and note-type personal computers have been on the increase. In order to realize the above requirements, it is effective to reduce the number of batteries mounted on the mobile device and to use a power circuit provided therein, wherein a booster switching regulator is often used. For the power circuit using a series regulator, a voltage-down switching regulator may be used in view of a high efficiency.
FIG. 1 is a circuit diagram illustrative of a first conventional switching regulator. FIG. 2 is a diagram illustrative of waveforms of j-point potential, f-point potential, d-point potential and g-point output of the first conventional switching regulator of FIG. 1. The first conventional switching regulator is of a pulse width modulation system wherein in place of simple comparison of a reference voltage to a comparative voltage, a potential difference between the reference voltage and the comparative voltage is amplified to obtain an amplified voltage, so that the amplified voltage is then compared with an output voltage of a triangle waveform by use of a comparator, whereby ON-OFF operations of switching transistors are made in accordance with a result of an output from the comparator.
Namely, the first conventional switching regulator has the following circuit elements. A power source 14 is provided for supplying a reference voltage to the first conventional switching regulator. An error-amplifier 19 is provided which has two inputs connected to an f-point which is connected to the power source 14 for receiving the reference voltage from the power source 14 and also connected to a d-point for receiving a comparative voltage, so that the error-amplifier 19 amplifies a difference in potential between the f-point and the d-point namely between the reference voltage from the power source 14 and the comparative voltage at the d-point to generate an amplified potential difference. A triangle-waveform generator 18 is also provided for generating a triangle waveform. The triangle-waveform generator 18 is connected to an h-point. A comparator 12 is also provided which has two inputs connected through the h-point to the triangle-waveform generator 18 for receiving the triangle waveform from the triangle-waveform generator 18 and also connected through a j-point to an output from the error-amplifier 19 for receiving the amplified potential difference from the error-amplifier 19, so that the comparator 12 compares the amplified potential difference with the triangle waveform. The comparator 12 has an output terminal connected to a g-point. A series connection of a p-channel output switching transistor 10 and an n-channel output switching transistor 9 is provided between an input terminal IN1 and a ground line, wherein the p-channel output switching transistor 10 is connected in series between the input terminal IN1 and the n-channel output switching transistor 9, whilst the n-channel output switching transistor 9 is connected in series between the ground line and the p-channel output switching transistor 10. Gates of the p-channel output switching transistor 10 and the n-channel output switching transistor 9 are connected through the g-point to the output terminal of the comparator 12. A k-point is a middle point between the p-channel output switching transistor 10 and the n-channel output switching transistor 9. A coil 5 is connected in series between the k-point and an output terminal OUT2. A load 3 is further provided which is connected between the output terminal OUT2 and the ground line, so that the load 3 is connected in series through the output terminal OUT2 to the coil 5. A capacitor 4 is also provided which is connected between the output terminal OUT2 and the ground line, so that the capacitor 4 is connected in series through the coil 5 to the k-point and also connected in series through the output terminal OUT2 to the load 3. A series connection of first and second resistances 7 and 8 is also connected between the ground line and a middle point between the coil 5 and the output terminal OUT2, so that the series connection of first and second resistances 7 and 8 is connected through the output terminal OUT2 to the load 3 and also connected through the coil 5 to the k-point. An intermediate point between the first and second resistances 7 and 8 is also connected through the d-point to the error-amplifier 19, so that the intermediate point between the first and second resistances 7 and 8 supplies the comparative voltage to the error-amplifier 19. The first resistance 7 is connected between the second resistance and the intermediate point between the coil 5 and the output terminal OUT2, whilst the second resistance 8 is connected between the ground line and the first resistance 7.
A potential difference between the reference voltage supplied through the f-point from the power source 14 and the comparative voltage supplied through the d-point from the intermediate point between the first and second resistances 7 and 8 is amplified by the error amplifier 19 to obtain an amplified potential difference, so that the amplified potential difference is then compared with the output voltage of the triangle waveform supplied through the h-point from the triangle waveform generator 18 by the comparator 12, whereby ON-OFF operations of the p-channel and n-channel switching transistors 10 and 9 are made in accordance with a result of the output from the comparator 12, wherein a duty ratio of the output waveform at the g-point connected to the output terminal of the comparator 12 is variable to realize a precise control thereof, whereby an output voltage with a small ripple appears at the output terminal OUT2.
The above first conventional switching regulator has the following disadvantages. The triangle waveform generator 18 and the error-amplifier 19 are essential for the above first conventional switching regulator. Further, a protection circuit is also necessary when the h-point potential and the g-point potential are outside the comparable range. This means that it is difficult to scale-down the circuit configuration of the first conventional switching regulator, and also that the circuit configuration is complicated whereby the power consumption is large. The efficiency of the voltage transformation as the power source circuit is also deteriorated.
FIG. 3 is a circuit diagram illustrative of a second conventional switching regulator. The second conventional switching regulator is of a pulse frequency modulation system wherein in place of simple comparison of a reference voltage to a comparative voltage, a potential difference between the reference voltage and the comparative voltage is amplified to obtain an amplified voltage, so that the amplified voltage is then compared with an output voltage of a triangle waveform by use of a comparator, whereby ON-OFF operations of a single switching transistor are made in accordance with a result of an output from the comparator.
Namely, the second conventional switching regulator has the following circuit elements. A power source 14 is provided for supplying a reference voltage to the first conventional switching regulator. An error-amplifier 19 is provided which has two inputs connected to an f-point which is connected to the power source 14 for receiving the reference voltage from the power source 14 and also connected to a d-point for receiving a comparative voltage, so that the error-amplifier 19 amplifies a difference in potential between the f-point and the d-point namely between the reference voltage from the power source 14 and the comparative voltage at the d-point to generate an amplified potential difference. A triangle-waveform generator 18 is also provided for generating a triangle waveform. The triangle-waveform generator 18 is connected to an h-point. A comparator 12 is also provided which has two inputs connected through the h-point to the triangle-waveform generator 18 for receiving the triangle waveform from the triangle-waveform generator 18 and also connected through a j-point to an output from the error-amplifier 19 for receiving the amplified potential difference from the error-amplifier 19, so that the comparator 12 compares the amplified potential difference with the triangle waveform. The comparator 12 has an output terminal connected to a point. A series connection of a coil 5 and an n-channel output switching transistor 9 is provided between an input terminal IN1 and a ground line, wherein the coil 5 is connected in series between the input terminal IN1 and the n-channel output switching transistor 9, whilst the n-channel output switching transistor 9 is connected in series between the ground line and the coil 5. A gates of the n-channel output switching transistor 9 is connected through the g-point to the output terminal of the comparator 12. A k-point is a middle point between the coil 5 and the n-channel output switching transistor 9. A diode 6 is connected in series between the k-point and an output terminal OUT2. A load 3 is further provided which is connected between the output terminal OUT2 and the ground line, so that the load 3 is connected in series through the output terminal OUT2 to the diode 6. A capacitor 4 is also provided which is connected between the output terminal OUT2 and the ground line, so that the capacitor 4 is connected in series through the diode 6 to the k-point and also connected in series through the output terminal OUT2 to the load 3. A series connection of first and second resistances 7 and 8 is also connected between the ground line and a middle point between the diode 6 and the output terminal OUT2, so that the series connection of first and second resistances 7 and 8 is connected through the output terminal OUT2 to the load 3 and also connected through the diode 6 to the k-point. An intermediate point between the first and second resistances 7 and 8 is also connected through the d-point to the error-amplifier 19, so that the intermediate point between the first and second resistances 7 and 8 supplies the comparative voltage to the error-amplifier 19. The first resistance 7 is connected between the second resistance and the intermediate point between the diode 6 and the output terminal OUT2, whilst the second resistance 8 is connected between the ground line and the first resistance 7.
A potential difference between the reference voltage supplied through the f-point from the power source 14 and the comparative voltage supplied through the d-point from the intermediate point between the first and second resistances 7 and 8 is amplified by the error amplifier 19 to obtain an amplified potential difference, so that the amplified potential difference is then compared with the output voltage of the triangle waveform supplied through the h-point from the triangle waveform generator 18 by the comparator 12, whereby ON-OFF operations of the n-channel switching transistor 9 are made in accordance with a result of the output from the comparator 12, wherein a duty ratio of the output waveform at the g-point connected to the output terminal of the comparator 12 is variable to realize a precise control thereof, whereby an output voltage with a small ripple appears at the output terminal OUT2.
The above second conventional switching regulator has the following disadvantages. The triangle waveform generator 18 and the error-amplifier 19 are essential for the above first conventional switching regulator. Further, a protection circuit is also necessary when the h-point potential and the g-point potential are outside the comparable range. This means that it is difficult to scale-down the circuit configuration of the first conventional switching regulator, and also that the circuit configuration is complicated whereby the power consumption is large. The efficiency of the voltage transformation as the power source circuit is also deteriorated.
FIG. 4 is a circuit diagram illustrative of a third conventional switching regulator. The third conventional switching regulator is of a pulse frequency modulation system wherein a potential difference between the reference voltage and the comparative voltage are compared with each other by use of a comparator, and an output from the comparator and an output voltage of a triangle waveform are inputted into a logic gate, for example, an AND-gate, whereby ON-OFF operations of a single switching transistor are made in accordance with an output from the logic gate, for example, the AND-gate.
Namely, the third conventional switching regulator has the following circuit elements. A power source 14 is provided for supplying a reference voltage to the first conventional switching regulator. A comparator 12 is provided which has two inputs connected to an f-point which is connected to the power source 14 for receiving the reference voltage from the power source 14 and also connected to a d-point for receiving a comparative voltage, so that the comparator 12 compares the reference voltage from the power source 14 and the comparative voltage at the d-point to generate an output. An oscillator 13 is also provided for generating a pulse waveform. The oscillator 13 is connected to a b-point. An AND-gate 11 is also provided which has two inputs connected through the b-point to the oscillator 13 for receiving the pulse-waveform from the oscillator 13 and also connected through a c-point to an output from the comparator 12 for receiving the output from the comparator 12, so that the AND-gate 11 performs the AND-operation of the pulse from the oscillator 13 and the output from the comparator 12. A series connection of a coil 5 and an n-channel output switching transistor 9 is provided between an input terminal IN1 and a ground line, wherein the coil 5 is connected in series between the input terminal IN1 and the n-channel output switching transistor 9, whilst the n-channel output switching transistor 9 is connected in series between the ground line and the coil 5. A gates of the n-channel output switching transistor 9 is connected through the a-point to the output terminal of the AND gate 11. A k-point is a middle point between the coil 5 and the n-channel output switching transistor 9. A diode 6 is connected in series between the k-point and an output terminal OUT2. A load 3 is further provided which is connected between the output terminal OUT2 and the ground line, so that the load 3 is connected in series through the output terminal OUT2 to the diode 6. A capacitor 4 is also provided which is connected between the output terminal OUT2 and the ground line, so that the capacitor 4 is connected in series through the diode 6 to the k-point and also connected in series through the output terminal OUT2 to the load 3. A series connection of first and second resistances 7 and 8 is also connected between the ground line and a middle point between the diode 6 and the output terminal OUT2, so that the series connection of first and second resistances 7 and 8 is connected through the output terminal OUT2 to the load 3 and also connected through the diode 6 to the k-point. An intermediate point between the first and second resistances 7 and 8 is also connected through the d-point to the comparator 12, so that the intermediate point between the first and second resistances 7 and 8 supplies the comparative voltage to the comparator 12. The first resistance 7 is connected between the second resistance and the intermediate point between the diode 6 and the output terminal OUT2, whilst the second resistance 8 is connected between the ground line and the first resistance 7.
A potential difference between the reference voltage supplied through the f-point from the power source 14 and the comparative voltage supplied from through the d-point from the intermediate point between the first and second resistances 7 and 8 are compared with each other by use of the comparator 12, and an output from the comparator 12 and an output voltage of the triangle waveform supplied through the b-point from the oscillator 13 are inputted into the logic gate, for example, the AND-gate 11, whereby ON-OFF operations of the single switching transistor 9 are made in accordance with an output from the logic gate, for example, the AND-gate 11.
The above third conventional switching regulator is of the pulse frequency modulation system, where the control to the output voltage is made in accordance with the number of the pulses, for which reason the circuit configuration is relatively simple, and the efficiency of voltage transformation as the power source circuit is also relatively high. However, the above third conventional switching regulator has the following disadvantages. The control to the output voltage is not precise as compared to the above pulse width modulation system. This means that the output voltage has a relatively large ripple.
In the above circumstances, it had been required to develop a novel switching regulator free from the above problem.